Semiconductor device and manufacturing method thereof

ABSTRACT

The present invention provides a semiconductor device which is characterized as follows. The semiconductor device includes: an interlayer insulating film formed above a semiconductor substrate and provided with a hole above an impurity diffusion region; a conductive plug formed in the hole and electrically connected to the impurity diffusion region; a conductive oxygen barrier film formed on the conductive plug and the interlayer insulating film around the conductive plug; a conductive anti-diffusion film formed on the conductive oxygen barrier film; and a capacitor that has a lower electrode which is formed on the conductive anti-diffusion film and which exposes platinum or palladium on the upper surface, a capacitor dielectric film made of a ferroelectric material, and an upper electrode. The conductive anti-diffusion film is made of a non-oxide conductive material for preventing the diffusion of the constituent element of the capacitor dielectric film.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/818,279, filed Jun. 18, 2010, which is a divisonal application ofU.S. application Ser. No. 11/938,958, filed Nov. 13, 2007, which is nowU.S. Pat. No. 7,763,921, issued Jul. 27, 2010, which is based on andclaims priority of Japanese Patent Application No. 2006-308159 filed onNov. 14, 2006, the entire contents of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a semiconductor device and amanufacturing method thereof.

BACKGROUND

Recently, along with advances in digital technologies, developments ofnon-volatile memories capable of saving a large volume of data at highrate are in progress.

A flash memory and a ferroelectric memory are known as such non-volatilememories.

Among them, a flash memory is provided with a floating gate buried in agate insulating film of an insulated gate field effect transistor(IGFET), and is configured to store information by accumulating chargesrepresenting stored information in this floating gate. However, such aflash memory has a drawback that it is necessary to apply a tunnelcurrent, which requires a relatively high voltage, to the gateinsulating film at the time of writing or erasing information.

In contrast, a ferroelectric memory, called also as a FeRAM (whichstands for a ferroelectric random access memory), is configured to storeinformation by utilizing a hysteresis property of a ferroelectric filmincluded in a ferroelectric capacitor. The ferroelectric film causespolarization depending on a voltage applied between an upper electrodeand a lower electrode of the capacitor, and spontaneous polarizationremains after the voltage is discontinued. This spontaneous polarizationis reversed when the polarity of the applied voltage is reversed. Theinformation is written in the ferroelectric film by causing thedirections of the spontaneous polarization to correspond respectively to“1” and “0”. The voltage required for writing the information therein islower than the voltage used in the flash memory. Moreover, the FeRAM hasanother advantage that it is possible to write the information at ahigher speed than that of the flash memory. By utilizing theseadvantages, an embedded chip, called a system-on-chip (SOC), formed bycombining a FeRAM and a logic circuit is now being examined for use inan IC card, for example.

Here, the crystalline orientation of the lower electrode of theferroelectric capacitor has a large impact on the ferroelectricproperties of a capacitor dielectric film such as an amount of residualpolarization charges. For this reason, in order to obtain aferroelectric capacitor having excellent electric properties, it isessential to control the crystalline orientation of the lower electrodeso as to improve the crystallinity thereof.

For example, the paragraph 0131 in Japanese Patent Application Laid-openPublication No. 2003-92391 (JP-A 2003-92391) discloses the technique touse the laminated film as the lower electrode, which is configured byforming an iridium film, an iridium oxide film, a platinum film, aplatinum oxide film and another platinum film in this order. JP-A2003-92391 discloses that it is possible to increase integratedintensity of the (111) orientation of the uppermost platinum film byforming the platinum film in the middle of the laminated film in thismanner.

The lowermost iridium film has a function as an antioxidant film for thetungsten plug located therebelow. Here, it is necessary to form theiridium film with a thickness of at least 200 nm in order to preventoxidation of the tungsten plug effectively. Consequently, this techniquehas a difficulty of patterning the lower electrode by etching.

Meanwhile, the paragraph 0027 in JP-A 2004-153006 discloses the samelower electrode structure as that in JP-A 2003-92391, which has the sameproblem as described above.

Moreover, the paragraph 0051 in JP-A 2003-318371 discloses the techniqueto form a lower electrode configured of a single-layer film orlaminated-layer film of a combination of an iridium film, an iridiumoxide film, a platinum film, a palladium film, a palladium oxide film,or a gold film.

Meanwhile, JP-A 2003-209179 discloses the technique to form an adhesivelayer below a lower electrode. The adhesive layer may include a titaniumoxide film, a platinum film, an iridium film, a zirconium film, atitanium film, a platinum oxide film, an iridium oxide film, a zirconiumoxide film, a titanium nitride film, a titanium aluminum nitride (TiAlN)film or the like (the paragraph 0087).

Moreover, JP-A 2003-51582 discloses the technique to form a barrierlayer made of an aluminum-iridium alloy on a plug, and then to form aplatinum film as the lower electrode on this barrier layer. According toJP-A 2003-51582, the aluminum oxide is formed in platinum crystal grainboundaries inside the platinum film by subjecting this platinum film tothermal treatment, and thereby a barrier characteristic of the barrierlayer against oxygen is enhanced (the paragraphs 0031 to 0034).

Meanwhile, JP-A Hei 6 (1994)-326270 discloses the technique to form atungsten film functioning as a diffusion barrier film below aferroelectric film made of PZT (lead zirconate titanate: PbZrTiO₃) inorder to prevent diffusion of lead atoms in the ferroelectric film (theparagraph 0041). However, tungsten is a material which is extremelysusceptible to oxidation. Consequently, there is a high risk of abnormaloxidation of the diffusion barrier film in an oxygen atmosphere whichleads to contact defects.

JP-A Hei 8 (1996)-288239 focuses on a fact that a platinum film is aptto transmit oxygen therethrough, and discloses the technique to form anoxygen barrier layer made of a titanium film below the lower electrodemade of platinum, and thereby oxygen is prevented from diffusing fromthe platinum film to the substrate (the paragraph 0006).

JP-A 2002-368200 discloses the technique to provide an adhesive layermade of hafnium-containing iridium between a diffusion barrier layer anda lower electrode formed on a contact plug in order to preventdetachment of the lower electrode (the paragraph 0061).

Moreover, JP-A 2002-57301 discloses the technique to form an oxygenbarrier layer between a tungsten plug and a lower electrode in theparagraphs 0023 and 0030. The oxygen barrier layer is formed either asthe laminated film of a titanium film and a titanium nitride film (theparagraph 0023) or as a titanium aluminum nitride film (the paragraph0030).

SUMMARY

According to one aspect of the present invention, there is provided asemiconductor device having an impurity diffusion region formed in asemiconductor substrate, an interlayer insulating film formed over thesemiconductor substrate and including a hole, a conductive plug formedin the hole and electrically connected to the impurity diffusion region,a conductive oxygen barrier film formed on the conductive plug and onthe interlayer insulating film around the conductive plug, a conductiveanti-diffusion film formed on the conductive oxygen barrier film, acapacitor including a lower electrode formed on the conductiveanti-diffusion film and exposing any of platinum and palladium on anupper surface, a capacitor dielectric film made of a ferroelectricmaterial, and an upper electrode, wherein the conductive anti-diffusionfilm is made of a non-oxide conductive material for preventing thediffusion of a constituent element of the capacitor dielectric film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a relationship obtained by examinationsbetween wafer numbers and integrated intensity of the (111) orientationof lead zirconate titanate (PZT) films.

FIG. 2 is a graph showing a relationship obtained by examinationsbetween the wafer numbers and ratio of the (222) orientation of the PZTfilms.

FIG. 3 is an illustration based on a scanning electron microscopic (SEM)image of the PZT film formed on an iridium film after heated in anoxygen atmosphere.

FIG. 4 is an illustration based on a SEM image obtained by forming a PZTinitial layer on a platinum film and forming a PZT film thereon by themetal-organic chemical vapor deposition (MOCVD) method.

FIG. 5 is an illustration based on a SEM image of the sample obtained byfurther forming a conductive oxygen barrier film 107 made of titaniumaluminum nitride on the structure of FIG. 4.

FIGS. 6A to 6X are cross-sectional views showing states in the course ofmanufacturing a semiconductor device according to a first embodiment ofthe present invention.

FIGS. 7A to 7L are cross-sectional views showing states in the course ofmanufacturing a semiconductor device according to a second embodiment ofthe present invention.

FIG. 8 is a cross-sectional view showing a semiconductor deviceaccording to a third embodiment of the present invention.

FIGS. 9A to 9Q are cross-sectional views showing states in the course ofmanufacturing a semiconductor device according to a fourth embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS (1) Process to Achieve theInvention

The process to achieve the present invention will be explained prior todescription of the preferred embodiments of the present invention.

The lead zirconate titanate (PZT) films formed by the sputtering methodand the metal-organic chemical vapor deposition (MOCVD) method aretypically used as capacitor dielectric films for ferroelectriccapacitors. Of those films, the PZT film formed by the MOCVD method hasan advantage in terms of higher integration as compared to filmsobtained by other film formation methods because the film iscrystallized at the time of film formation, and thus hardly reduces aswitching charge amount Qsw even when the film thickness is reduced.

In the MOCVD method, a silicon substrate is put in a reaction chamber,and is heated up to a predetermined substrate temperature. Some gasesare conceivable for the atmosphere in the reaction chamber when raisingthe temperature.

Nevertheless, it is found out that the crystallinity of the PZT film issubstantially degraded when an argon atmosphere is used as theatmosphere. For example, while the largest polarization in a PZT crystalis observed in the (111) direction, the PZT film formed after heated inthe argon atmosphere is oriented in the (100) direction or the (101)direction. Such a PZT crystal exhibits a small switching charge amount,and complicates writing or reading information in and out of the memoryusing such a ferroelectric capacitor.

To avoid such an inconvenience, the present inventor has thought aboutheating a silicon substrate in an oxygen atmosphere before forming thePZT film.

However, there are two problems as follows in the case of heating thesubstrate in such an oxygen atmosphere if an iridium film is used as alower electrode.

Specifically, a first problem is that the directions of the crystallineorientation of the PZT film fluctuate every time when the PZT film isformed.

FIG. 1 is a graph showing a relationship obtained by examinationsbetween silicon wafer numbers and integrated intensity of the (111)orientation of the PZT films. Note that the silicon wafer numbers arearranged in the order of formation of the PZT films (in the processingorder).

As shown in FIG. 1, the integrated intensity of the (111) orientationfluctuates widely among the wafers.

Meanwhile, FIG. 2 is a graph showing a relationship obtained byexaminations between the silicon wafer numbers and ratio of the (222)orientation of the PZT films. Note that the rate of the (222)orientation is defined asI_((2,2,2))/(I_((1,0,0,))+I(_(1,0,1))+I_((2,2,2))), where I_((nx,ny,nz))denotes the integrated intensity in the (n_(x), n_(y), n_(z)) direction.

As shown in FIG. 2, the ratio of the (222) orientation also fluctuateamong the wafers.

If the crystalline orientation of the PZT films widely fluctuates amongthe wafers as shown in FIG. 1 and FIG. 2, it is not possible tomass-produce ferroelectric capacitors having uniform characteristics.

Meanwhile, a second problem in the case of heating the substrate in theoxygen atmosphere is large unevenness that appears on the surface of thePZT film.

FIG. 3 is an illustration based on a scanning electron microscopic (SEM)image of such a PZT film.

In this example, an iridium film 101 is formed on a silicon substrate100, and then a PZT film 102 is formed on the iridium film 101 by theMOCVD method.

As shown in the illustration, large unevenness is observed on thesurface of the PZT film 102. One of conceivable reasons is that thesilicon substrate 100 is heated in the oxygen atmosphere before the PZTfilm 102 is formed, and consequently a thin iridium oxide layer isformed on the surface of the iridium film 101. The iridium oxide layerreturns to original iridium as a result of the reduction reaction bycontact with the solvent such as tetrahydrofuran (THF) or butyl acetatesupplied at the time of forming the PZT film 102. However, the iridiumoxide layer also contains abnormally oxidized iridium oxide which is notreduced by the above-mentioned solvent, and which remains as iridiumoxide. As a consequence, the surface of the iridium film 101 includes aheterogeneous phase that makes up of the iridium oxide, resulting in therough surface of the PZT film 102.

It is conceivable that the fluctuation in the crystalline orientation ofthe PZT films shown in FIG. 1 and FIG. 2 is also attributed to theabnormal oxidation of the iridium oxide film.

The present inventor has conducted further studies to avoid suchproblems.

As a result, the present inventor has found out that the problem of therough surface of the PZT film could be resolved by firstly forming athin initial layer of the PZT film on the iridium film by the sputteringmethod or the sol-gel method, and then forming the PZT film on thisinitial layer by the MOCVD method.

Here, the initial layer of the PZT film formed by the sputtering methodor the sol-gel method is not crystallized, and consequently the layer isamorphous immediately after the film formation. Therefore, prior to theformation of the PZT film by the MOCVD method, it is necessary tocrystallize the initial layer by subjecting the initial layer tocrystallization annealing.

However, it was found out that the crystallinity of the initial layerformed on the iridium film by the sputtering method or the sol-gelmethod was extremely poorer than the crystallinity of the PZT filmformed by the MOCVD method. One of conceivable reasons is that the PZTinitial layer is not favorably crystallized by crystallization annealingdue to a difference in the lattice constant between iridium and PZT.

To improve the crystallinity of the PZT initial layer, it is effectiveto constrict a lower electrode from platinum, having a closer latticeconstant to that of PZT than iridium, instead of the iridium film, andthen to form the PZT initial layer on the lower electrode.

FIG. 4 is an illustration based on a SEM image obtained by forming a PZTinitial layer on a platinum film and forming a PZT film thereon by theMOCVD method.

In this example, a platinum film 105 is formed on a silicon substrate100. Then, although the PZT initial layer is too thin to observe in theillustration, the PZT initial layer is formed with a thickness of about30 nm on the platinum film 105 by the sputtering method. Thereafter, aPZT film 106 is formed thereon with a thickness of about 100 nm by theMOCVD method.

As shown in FIG. 4, it is possible to achieve the smooth surfacemorphology of the PZT film 106 by covering the platinum film 105 withthe PZT initial layer.

This is attributed to the fact that the surface of the platinum film 105is covered with the PZT initial layer and is thus hardly oxidized evenwhen the silicon substrate 100 is heated in the oxygen atmosphere beforethe PZT film 106 is formed by the MOCVD method. Accordingly, noheterogeneous phase is generated on the surface, except for that ofplatinum.

Moreover, since the PZT initial layer and the platinum film 106 havemutually close lattice constants, it is also possible to preventdeterioration in the crystallinity of the PZT film 106 associated withlattice mismatch.

On the other hand, the substrate is heated to a high temperature ofabout 620° C. in the MOCVD method. Accordingly, if the PZT film 106 isformed directly on the platinum film 105, there arises another problemof reduction in the switching charge amount of the PZT film 106attributable to the reaction between lead atoms in the PZT film 106 andthe platinum film 105 caused by the temperature at the time of the filmformation.

In contrast, according to the sputtering method, it is possible to formthe PZT film at a lower temperature, such as room temperature, than inthe MOCVD method. Thus, even when the PZT initial layer is formed by thesputtering method as described above, it is possible to suppress thereaction between the lead and the platinum film 105. Moreover, the PZTinitial layer functions as a lead barrier layer when the PZT film 106 isformed by the MOCVD method. Accordingly, it is also possible to suppressthe reaction between the lead in the PZT film 106 and the platinum film105.

Incidentally, ferroelectric random access memories (FeRAMs) are broadlycategorized into a stack type and a planar type based on theirstructures.

Of these types, the stack type FeRAM has the structure in which thelower electrode is formed directly on a conductive plug. This FeRAM isformed by patterning the lower electrode, a capacitor dielectric film,and an upper electrode by means of collective etching. Accordingly, thisFeRAM has the small area of the capacitor, and is therefore advantageousfor higher integration.

Nevertheless, in the case of the stack type FeRAM, it is necessary toform a conductive oxygen barrier film such as a titanium aluminumnitride film between the conductive plug and the lower electrode inorder to prevent the oxidation of the conductive plug locatedimmediately below the capacitor.

FIG. 5 is an illustration based on a SEM image of the sample obtained byfurther forming a conductive oxygen barrier film 107 made of titaniumaluminum nitride on the structure of FIG. 4.

As shown in FIG. 5, the platinum film 105 is detached from theconductive oxygen barrier film 107 in this sample. One of conceivablereasons is that the platinum film 105 is apt to transmit lead atoms.Accordingly, the lead atoms in the PZT initial layer are transmittedthrough the platinum film 105 in the course of subjecting the PZTinitial layer to crystallization annealing, whereby lead compounds areformed on an interface between the platinum film 105 and the conductiveoxygen barrier film 107.

Note that, in addition to the above-described crystallization annealingprocess, the annealing process, for example, on the upper electrode mayalso cause the thermal diffusion of the lead atoms. Although thedetachment of the platinum film 105 is observed in this example, theremay be another case where the expansion of the platinum film 105 isobserved.

The present inventor has contemplated effective measures for preventingthe detachment between the conductive barrier film and the lowerelectrode in the case of using the lead-transmissive film represented bythe aforementioned platinum film as the lower electrode and forming thePZT initial layer on the lower electrode. As a consequence, the presentinventor has accomplished the embodiments of the present inventiondescribed hereinbelow.

(2) First Embodiment

FIGS. 6A to 6X are cross-sectional views showing states in the course ofmanufacturing a semiconductor device according to a first embodiment.

This semiconductor device is a stack type FeRAM which is advantageousfor miniaturization. The semiconductor device is manufactured asdescribed below.

In the beginning, processes to be conducted prior to obtaining across-sectional structure shown in FIG. 6A will be described below.

First, a groove for the shallow trench isolation (STI) to define theactive region of a transistor is formed in a surface of a silicon(semiconductor) substrate 1 either of an n type or a p type, and aninsulating film such as silicon oxide is buried therein to form anelement isolation insulating film 2. Note that the element isolationstructure is not limited only to the STI. It is also possible to formthe element isolation insulating film 2 by the local oxidation ofsilicon (LOCOS) method instead.

Next, a p-type impurity is doped in the active region of the siliconsubstrate 1 to form a p-well 3. Then, a thermal oxide film, which is toconstitute a gate insulating film 4, is formed by subjecting the surfaceof the active region to thermal oxidation.

Subsequently, an amorphous or polycrystalline silicon film is formed onthe entire upper surface of the silicon substrate 1, and two gateelectrodes 5 are formed by patterning these films usingphotolithography.

The gate electrodes 5 are arranged in parallel on the p-well 3 at adistance from each other. The gate electrodes 5 constitute part of wordlines.

Next, an n-type impurity is doped on portions of the silicon substrates1 beside the gate electrodes 5 by means of ion implantation while thegate electrodes 5 are used as the mask, thereby first and secondsource/drain extensions 6 a and 6 b are formed.

Thereafter, an insulating film is formed on the entire upper surface ofthe silicon substrate 1, and the insulating film is etched back so as toform insulative sidewalls 7 beside the gate electrodes 5. As for theinsulating film, a silicon oxide film is formed by the CVD method, forexample.

Subsequently, ions of n-type impurity are implanted again into thesilicon substrate 1 while the insulative side walls 7 and the gateelectrodes 5 are used as the mask, thereby first and second source/drainregions (first and second impurity diffusion regions) 8 a and 8 b areformed at a distance from each other, on the surface layer of thesilicon substrate 1 beside the gate electrodes 5.

By completing these steps, first and second metal oxide silicon (MOS)transistors TR₁ and TR₂, which include the gate insulating film 4, thegate electrodes 5, and the first and second source/drain regions 8 a and8 b, are formed in the active region of the silicon substrate 1.

Next, after a refractory metal layer such as a cobalt layer is formed onthe entire upper surface of the silicon substrate 1 by the sputteringmethod, this refractory metal layer is heated to cause a reaction withsilicon. In this way, a refractory metal silicide layer 9 is formed onthe silicon substrate 1. The refractory metal silicide layer 9 is alsoformed on the top layer portion of the gate electrodes 5. Accordingly,resistances of the gate electrodes 5 are reduced.

Thereafter, the unreacted refractory metal layer located above theelement isolation insulating film 2, for example, is removed by wetetching.

Subsequently, a silicon nitride (SiN) film is formed with a thickness ofabout 80 nm on the entire upper surface of the silicon substrate 1 bythe plasma CVD method. This SiN film is formed as a cover insulatingfilm 10. Next, a silicon oxide film serving as a first interlayerinsulating film 11 is formed with a thickness of about 1000 nm on thiscover insulating film 10 by the plasma CVD method usingtetraethylorthosilicate (TEOS) gas.

Next, the upper surface of the first interlayer insulating film 11 ispolished and planarized by the chemical mechanical polishing (CMP)method. As a result of this CMP process, the thickness of the firstinterlayer insulating film 11 becomes approximately equal to 700 nm on aflat surface of the silicon substrate 1.

Then, contact holes each having a diameter of 0.25 μm are formed abovethe first and second source/drain regions 8 a and 8 b by patterning thecover insulating film 10 and the first interlayer insulating film 11using the photolithography. In addition, a glue film (an adhesive film)and a tungsten film are sequentially formed inside each of the contactholes, and the excessive glue film and the excessive tungsten film onthe first interlayer insulating film 11 are polished and removed by theCMP method. In this way, these films are left only inside the contactholes as first and second conductive plugs 32 a and 32 b.

These first and second conductive plugs 32 a and 32 b are electricallyconnected to the first and second source/drain regions 8 a and 8 b,respectively.

Note that the glue film is obtained by forming a titanium film with athickness of about 30 nm and a titanium nitride film with a thickness ofabout 20 nm in this order. Meanwhile, the tungsten film before the CMPprocess has a thickness of about 300 nm on the first interlayerinsulating film 11.

Here, the first and second conductive plugs 32 a and 32 b are mademainly of tungsten which is susceptible to oxidation. Therefore, theconductive plugs may cause contact defects if tungsten is oxidizedduring the process.

To deal with this problem, a silicon oxynitride (SiON) film is formedwith a thickness of about 130 nm on the conductive plugs 32 a and 32 band the first interlayer insulating film 11 by the plasma CVD method asan antioxidant insulating film 14 for preventing oxidation of theseplugs 32 a and 32 b.

Note that, instead of the silicon oxynitride film, it is also possibleto form a silicon nitride (SiN) film or an alumina film as theantioxidant insulating film 14.

Thereafter, a silicon oxide film is formed with a thickness of about 300nm on the antioxidant insulating film 14 by the plasma CVD method usingthe TEOS gas. This silicon oxide film is formed as an underlyinginsulating film 15.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 6B will be described below.

First, first holes 15 a are formed in the underlying insulating film 15and the antioxidant insulating film 14 located above the firstconductive plugs 32 a by patterning these insulating films.

Next, a titanium nitride film functioning as a glue film 35 is formed onthe inner surfaces of the first holes 15 a and on the underlyinginsulating film 15 by the sputtering method.

Moreover, a tungsten film functioning as a plug conductive film 36 isformed on this glue film 35 by the CVD method, thereby the first holes15 a are completely buried with this plug conductive film 36.

Subsequently, excessive portions of the glue film 35 and the plugconductive film 36 on the underlying insulating film 15 are polished andremoved by the CMP method as shown in FIG. 6C. In this way, the gluefilm 35 and the plug conductive film 36 are left inside the first holes15 a as third conductive plugs 36 a which are electrically connected tothe first conductive plugs 32 a.

This CMP process applies slurry such as W2000 manufactured by CabotMicroelectronics Corporation, which is configured to render a polishingspeed of the glue film 35 and the plug conductive film 36 beingpolishing targets faster than a polishing speed of the underlyinginsulating film 15 located therebelow. Moreover, in order not to leavean unpolished portion on the underlying insulating film 15, thepolishing amount in this CMP process is set to be thicker than the totalthickness of the films 35 and 36. In other words, this CMP process isconducted as an overpolishing process.

Next, as shown in FIG. 6D, the underlying insulating film 15 made ofsilicon oxide is exposed to nitrogen-containing plasma such as ammonia(NH₃) plasma, thereby a NH group is bonded to each oxygen atom on thesurface of the underlying insulating film 15.

In this ammonia plasma process, a parallel-plate plasma reactor is used.The reactor includes an opposing electrode which is located by about 9mm (350 mils) away from the silicon substrate 1, for example. Then, theprocess is executed by supplying ammonia gas into a chamber at a flowrate of 350 sccm while maintaining a substrate temperature at 400° C.under a pressure of 266 Pa (2 Torr), and supplying high-frequency powerof 100 W at a frequency of 13.56 MHz to the silicon substrate 1 whilesupplying high-frequency power of 55 W at a frequency of 350 kHz to theabove-mentioned opposing electrode for 60 seconds.

Subsequently, a titanium film is formed with a thickness of about 20 nmon the underlying insulating film 15 and the third conductive plugs 36 aas shown in FIG. 6E. This titanium film is formed as a conductiveadhesive film 16.

The conditions for forming this conductive adhesive film 16 are notparticularly limited. However, in this embodiment, the substratetemperature is set equal to 20° C. in an argon atmosphere at 0.15 Pa byuse of the sputter chamber configured to set a distance between thesilicon substrate 1 and a titanium target equal to 60 mm. Then, theconductive adhesive film 16 made of titanium is formed by supplyingdirect-current (DC) power at 2.6 kW to the chamber for 5 seconds.

Here, since the ammonia plasma process (see FIG. 6D) is carried out inadvance to bond the NH groups to the oxygen atoms on the surface of theunderlying insulating film 15, the titanium atoms deposited on theunderlying insulating film 15 are hardly captured by the oxygen atoms onthe surface of the underlying insulating film 15. Accordingly, thetitanium atoms can move freely on the surface of the underlyinginsulating film 15, and it is therefore possible to form the conductiveadhesive film 16 made of titanium which is highly self-organized in the(002) direction.

Thereafter, the conductive adhesive film 16 is subjected to rapidthermal annealing (RTA) in a nitrogen atmosphere at a substratetemperature of 650° C. for a processing period of 60 seconds. In thisway, the conductive adhesive film 16 made of the titanium isnitrogenized, whereby the conductive adhesive film 16 is formed of thetitanium nitride which is oriented in the (111) direction.

Here, the material of the conductive adhesive film 16 is not limitedonly to titanium nitride. The conductive adhesive film 16 may be made ofany of titanium, titanium nitride, platinum, iridium, rhenium,ruthenium, palladium, rhodium and osmium, or an alloy thereof.Alternatively, it is possible to form the conductive adhesive film 16 byuse of any of platinum oxide, iridium oxide, ruthenium oxide andpalladium oxide.

Next, as shown in FIG. 6F, a titanium aluminum nitride (TiAlN) filmfunctioning as a conductive oxygen barrier film 17 is formed with athickness of 100 nm on this conductive adhesive film 16 by the reactivesputtering method.

The conductive oxygen barrier film 17 made of titanium aluminum nitridehas an excellent oxygen transmission blocking function, and plays a rolefor preventing the occurrence of contact defects attributable to theoxidation of the third conductive plugs 36 a located therebelow.

The conditions for forming this conductive oxygen barrier film 17 arenot particularly limited. However, in this embodiment, an alloy targetcontaining titanium and aluminum is used, and also the mixed gas ofargon and nitrogen is used as sputtering gas. Moreover, the conductiveoxygen barrier film 17 is formed under the conditions of a flow rate ofargon gas equal to 40 sccm, a flow rate of nitrogen gas equal to 100sccm, a pressure at 253.3 Pa, a substrate temperature at 400° C., andsputtering power equal to 1.0 kW.

In addition, the material of the conductive oxygen barrier film 17 isnot limited only to titanium aluminum nitride. The conductive oxygenbarrier film 17 may be made of any of titanium aluminum nitride,titanium aluminum oxynitride (TiAlON), tantalum aluminum nitride(TaAlN), and tantalum aluminum oxynitride (TaAlON).

The conductive oxygen barrier film 17 has enhanced adhesion strength tothe films located below by the conductive adhesive film 16. Note that,it is possible to omit the conductive adhesive film 16 if the adhesionstrength is not a serious problem. In that case, the conductive oxygenbarrier film 17 is directly formed on each of the upper surfaces of thethird conductive plugs 36 a and the underlying insulating films 15.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 6G will be described below.

First, a titanium film functioning as a conductive anti-diffusion film22 is formed with a thickness ranging from 10 nm to 100 nm, for examplewith a thickness of about 50 nm, on the conductive oxygen barrier film17 by the sputtering method.

The conditions for forming this titanium film are not particularlylimited. In this embodiment, a sputtering chamber is used to form thetitanium film. The sputtering chamber is configured to set a spacebetween the silicon substrate 1 and a titanium target equal to 60 mm.Moreover, the above-mentioned titanium film is formed under an argonatmosphere at 0.15 Pa by applying DC power of 2.6 kW to the sputteringatmosphere for 13 seconds while the substrate temperature is maintainedat 150° C.

Since titanium has a self-orienting property, the conductiveanti-diffusion film 22 made of titanium is crystallized at the time offilm formation. The crystalline orientation of the conductiveanti-diffusion film 22 is typically in the (002) direction.

Next, the conductive anti-diffusion film 22 is subjected to RTA in anitrogen atmosphere at a substrate temperature of 650° C. In this way,the titanium in the conductive anti-diffusion film 22 is nitrogenized,whereby the conductive anti-diffusion film 22 is formed of titaniumnitride.

By such a nitrogenizing process, the crystalline orientation of titaniumnitride is typically aligned in the (111) direction.

Note that, although the conductive anti-diffusion film 22 made oftitanium nitride is formed by nitrogenizing the titanium film in thisembodiment, the method for forming the titanium nitride film is notlimited only to the foregoing method.

For example, it is possible to form the titanium nitride film by thereactive sputtering method configured to sputter a titanium target innitrogen gas. In this case, the mixed gas of the argon gas at a flowrate of 50 sccm and the nitrogen gas at a flow rate of 20 sccm is usedas sputtering gas. Moreover, the titanium nitride film with a thicknessof 50 nm can be obtained by applying DC power of 8.3 kW to thesputtering atmosphere for 22 seconds while the substrate temperature ismaintained at 200° C.

Subsequently, a platinum film serving as a first conductive film 23 isformed with a thickness of about 100 nm on this conductiveanti-diffusion film 22 by the sputtering method.

This platinum film can be formed by maintaining the substratetemperature at 400° C. in an argon atmosphere at a pressure of 0.2 Paand applying sputtering power of 0.5 kW to the sputtering atmosphere,for example.

Thereafter, the first conductive film 23 is subjected to RTA in theargon atmosphere for 60 seconds while the substrate temperature is setequal to or above 650° C. By performing this RTA process, the adhesionamong the first conductive film 23, the conductive anti-diffusion film22, and the conductive oxygen barrier film 17 is enhanced, and thecrystallinity of the first conductive film 23 is also improved. Notethat it is also possible to perform this RTA process in a nitrogenatmosphere instead of the argon atmosphere.

Here, since the conductive anti-diffusion film 22 is oriented in the(111) direction as described above, the crystalline orientation of thefirst conductive film 23 is also aligned in the (111) direction by meansof this orientation.

Note that, although the platinum film is formed as the first conductivefilm 23 in this embodiment, it is also possible to form a palladium filmas the first conductive film 23 instead. It is also conceivable to formthe first conductive film 23 with a film made of any other platinumgroup elements. Nevertheless, the elements other than platinum andpalladium exhibit the significant lattice mismatch with PZT to bedescribed later, and thereby the crystallinity of PZT is degraded.

For example, as the lattice constant of PZT is equal to 3.96 Å, platinumhaving the lattice constant of 3.9 Å exhibits less lattice mismatch withPZT than iridium having the lattice constant of 3.8 Å, and thus improvesthe crystallinity of PZT. Accordingly, it is not favorable to form thefirst conductive film 23 as a single-layer film made of the otherplatinum group elements such as iridium.

Nevertheless, it is possible to form the first conductive film 23 as thelaminated-layer film configured to expose either platinum or palladiumon the upper surface, or namely, as the laminated-layer film havingeither a platinum film or a palladium film formed on the uppermostlayer. In this case, it is possible to form a platinum oxide film or aplatinum-containing alloy film as part of the first conductive film 23below the platinum film or the palladium film.

Next, as shown in FIG. 6H, a thin PZT initial layer is formed with athickness ranging, for example, from about 1 nm to about 50 nm, ortypically from 20 nm to 30 nm, on the first conductive film 23 by thesputtering method. This PZT initial layer is formed as a firstferroelectric film 24 b.

Here, one of reasons for setting the upper limit thickness of the firstferroelectric film 24 b to 50 nm is that, if the first ferroelectricfilm 24 b is formed with a thickness of greater than 50 nm, an electricfield to be applied to the first ferroelectric film 24 b becomes tooweak at the time of operating the FeRAM, and consequently it isdisadvantageous in light of low-voltage operation of the FeRAM.Moreover, it is favorable to form the first ferroelectric film 24 b in athickness equal to or below 50 nm in order to prevent a decrease in aswitching charge amount Qsw of the first ferroelectric film 24 b.

Meanwhile, if the film formation temperature of the first ferroelectricfilm 24 b is too high, the platinum in the first conductive film 23reacts with the lead in the first ferroelectric film 24 b as describedpreviously, which may lead to the risk of the decrease in the switchingcharge amount of the first ferroelectric film 24 b even when the firstferroelectric film 24 b is subjected to crystallization annealing to bedescribed later.

For this reason, it is preferable to set the film formation temperatureof the first ferroelectric film 24 b as low as possible, such as atemperature equal to or below 80° C. In this embodiment, the firstferroelectric film 24 b is formed at room temperature.

In addition to the sputtering method, another film formation methodcapable of forming the first ferroelectric film 24 b at such a lowtemperature is the sol-gel method. Accordingly, the first ferroelectricfilm 24 b may be formed by this sol-gel method.

On the contrary, in the MOCVD method, it is necessary to set thesubstrate temperature to a high temperature around 620° C. when formingthe PZT film. Consequently, if the first ferroelectric film 24 b isformed by the MOCVD method, the ferroelectric properties of the firstferroelectric film 24 b such as the switching charge amount is degradedby the above-described reaction between the lead and the platinum.

After all, as the method of forming the first ferroelectric film 24 b,it is preferable to use any of the sputtering method and the sol-gelmethod, which does not require the substrate heating. On the other hand,it is not favorable to use the MOCVD method that requires the substrateheating.

Here, in addition to the advantage capable of forming the firstferroelectric film 24 b at a low temperature, the sputtering method alsohas an advantage that it is easier to dope a small amount of additiveelement to the first ferroelectric film 24 b.

Utilizing such an advantage, it is preferable to add any of lanthanum,calcium, strontium, and niobium at a concentration in a range from 0.1mol % to 5 mol % to PZT when forming the first ferroelectric film 24 b.By using the first ferroelectric film 24 b doped with any of theseelements to a capacitor to be described later, it is possible to obtaineffects such as improvement in fatigue-resistant and imprintcharacteristics of the capacitor, reduction in a leak current, andreduction in an operating voltage.

In this embodiment, the switching charge amount of the firstferroelectric film 24 b is increased by doping calcium, lanthanum, andstrontium at concentrations of 5 mol %, 2 mol %, and 2 mol %,respectively, to PZT. It is to be noted that the PZT doped withlanthanum may also be referred to as PLZT.

Moreover, the material of the first ferroelectric film 24 b is notlimited only to PZT as long as it is a ferroelectric material having anABO₃-type perovskite structure (in which A is any one selected from thegroup consisting of Bi, Pb, Ba, Sr, Ca, Na, K and any of rare earthelements, and B is any one selected from the group consisting of Ti, Zr,Nb, Ta, W, Mn, Fe, Co and Cr).

Such a ferroelectric material satisfying the above-mentioned structureis BLT ((Bi, La)₄Ti₃O₁₂), for example.

In addition, Bi layer-structure compounds such as (Bi_(1−x)R_(x))Ti₃O₁₂(in which R is a rare earth element and 0<x<1), SrBi₂Ta₂O₉ (SBT),SrBi₄Ti₄O₁₅, and the like are usable as the constituent material of thefirst ferroelectric film 24 b since these substances have the ABO₃-typeperovskite structure when seen as one unit of crystal.

Incidentally, the first ferroelectric film 24 b formed by the sputteringmethod as described above is not crystallized, and consequently is notdirectly usable as a capacitor dielectric body due to its small residualpolarization charge amount.

To deal with this problem, in the next step, the first ferroelectricfilm 24 b is crystallized by annealing as shown in FIG. 6I to align thecrystalline orientation of PZT in the (111) direction that maximizes thepolarization amount. Such an annealing process is also called ascrystallization annealing.

The conditions for the crystallization annealing process are notparticularly limited. However, in this embodiment, the substratetemperature is set in a range from 550° C. to 800° C., for example at580° C. in the mixed gas atmosphere of oxygen and argon, and a thermaltreatment period is set in a range from 30 to 120 seconds, for examplefor 90 seconds. Here, the flow rate of oxygen is set in a range from 0sccm to 25 sccm, and the flow rate of argon is set 2000 sccm.

The optimal substrate temperature in the crystallization annealingprocess depends on the material of the first ferroelectric film 24 b.For example, when the first ferroelectric film 24 b is made of PZT orPZT doped with a small amount of an additive element, the substratetemperature is preferably set equal to or below 600° C. Meanwhile, whenthe first ferroelectric film 24 b is made of BLT, the substratetemperature is preferably set equal to or below 700° C. When the firstferroelectric film 24 b is made of SBT, the substrate temperature ispreferably set equal to or below 800° C.

Note that the direction of the crystalline orientation of the PZT filmafter the crystallization annealing process depends on the filmformation temperature in the course of sputtering the PZT film. Forexample, if the film formation temperature of the PZT film is higherthan 80° C., the PZT film after crystallization annealing is oriented inthe (101) direction. Consequently, it is difficult to align thecrystalline orientation in the (111) direction to achieve a highpolarization amount.

For this reason, it is preferable to form the first ferroelectric film24 b made of PZT by the sputtering method configured to set thesubstrate temperature equal to or below 80° C., for example at roomtemperature (20° C.) from the viewpoint of increasing the polarizationamount as well.

Moreover, since the conductive anti-diffusion film 22 is oriented in the(111) direction as described previously, the first conductive film 23thereon is also oriented in the (111) direction. As the first conductivefilm 23 located below the first ferroelectric film 24 b is oriented inthe (111) direction in this manner, the crystalline orientation of thefirst ferroelectric film 24 b is easily aligned in the (111) directionby this crystallization annealing.

Incidentally, in the ferroelectric material of the ABO₃-type perovskitestructure constituting the first ferroelectric film 24 b, the atoms onthe A site tend to be thermally diffused downward in the firstferroelectric film 24 b by such a crystallization annealing. Forexample, when the PZT film is used as the first ferroelectric film 24 bas described above, the lead atoms tend to be thermally diffuseddownward.

The first conductive film 23 formed below the first ferroelectric film24 b contains platinum or palladium. Such materials are apt to transmitthe atoms on the A site such as lead. Accordingly, the lead atoms can bediffused into the first conductive film 23 from the first ferroelectricfilm 24 b by crystallization annealing.

Nevertheless, since the conductive anti-diffusion film 22 is formedbelow the first conductive film 23 in this embodiment, the diffusion ofthe lead atoms is blocked by the conductive anti-diffusion film 22.

As a result, the lead atoms are not thermally diffused on the interfacebetween the conductive oxygen battier film 17 and the conductiveanti-diffusion film 22. In other words, no lead exists on thatinterface. It is, therefore, possible to prevent detachment or expansionof the first conductive film 23 attributable to the reaction between theconductive oxygen barrier film 17 and lead as illustrated in FIG. 5.

Next, as shown in FIG. 6J, a PZT film is formed with a thickness ofabout 80 nm on the first ferroelectric film 24 b by the MOCVD method.This PZT film is formed as a second ferroelectric film 24 c. The secondferroelectric film 24 c formed by the MOCVD method is crystallized andthe crystalline orientation thereof is aligned in the (111) direction atthe time of film formation. Thus, it is not necessary to execute thecrystallization annealing process to crystallize the secondferroelectric film 24 c afterward.

Here, unlike the sputtering method, the switching charge amount Qsw ofthe capacitor is significantly reduced if an additive element such aslanthanum, calcium, strontium or niobium is added to PZT in the courseof the MOCVD method. Accordingly, in the MOCVD method, it is preferableto form the second ferroelectric film 24 c of pure PZT without addingany of these elements to the PZT.

The MOCVD method is conducted as follows.

First, the silicon substrate 1 is placed on the susceptor in theunillustrated reaction chamber.

Subsequently, oxygen is introduced to the reaction chamber at a flowrate of 2 slm, and the silicon substrate 1 is heated so as to stabilizethe substrate temperature around 620° C.

Even if the temperature is heated in the oxygen atmosphere in thismanner, the first conductive film 23 does not cause abnormal oxidationbecause the upper surface of the first conductive film 23 is coveredwith the first ferroelectric film 24 b. It is, therefore, possible tosuppress the surface roughness of the PZT film or the fluctuation in thecrystalline orientation of the PZT film attributable to the abnormaloxidation of the first conductive film 23.

Then, a vaporized THF solvent is introduced to the reaction chamber. Inthis way, the first ferroelectric film 24 b is exposed to the solventgas atmosphere.

By supplying the solvent gas before supplying the raw material gas inthis manner, it is possible to prevent the solidification of rawmaterial gas inside vaporizers and pipes, and to avoid the clogging ofpipes and the like. Note that it is also possible to use vaporized butylacetate as the solvent gas instead of THF.

Thereafter, the raw material gases are prepared by vaporizing respectiveliquid raw materials of Pb, Zr, and Ti with vaporizers, and theformation of the PZT film is started by introducing the respective rawmaterial gases into the reaction chamber.

Here, the respective liquid raw materials can be prepared by dissolving,for example, Pb(DPM)₂ (chemical formula: Pb(C₁₁H₁₉O₂)₂), Zr(dmhd)₄(chemical formula: Zr(C₉H₁₅O₂)₄), and Ti(O-iOr)₂(DPM)₂ (chemicalformula: Ti(C₃H₇O)₂(C₁₁H₁₉O₂)₂) into THF (tetrahydrofuran: C₄H₈O)solvents at a concentration of 0.3 mol/l, respectively. Here, the flowof the respective vaporized raw material gases is not particularlylimited. In this embodiment, the liquid raw materials are vaporized bysupplying them to vaporizers at the flow of 0.326 ml/min, 0.200 mil/min,and 0.200 ml/min, respectively, to obtain the Pb, Zr, and Ti rawmaterial gases.

Thereafter, the PZT film is formed with a thickness of 80 nm bymaintaining the aforementioned state approximately for 620 seconds undera pressure of 665 Pa (5 Torr).

In this way, the silicon substrate 1 is heated to a high temperaturearound 620° C. at the time of forming the second ferroelectric film 24 cby the MOCVD method. However, since the first ferroelectric film 24 b isformed below the second ferroelectric film 24 c in advance, the firstferroelectric film 24 b inhibits the movement of the lead atoms in thesecond ferroelectric film 24 c to the first conductive film 23 due tothe heat. Accordingly, the above-mentioned reaction between the lead andthe platinum in the first conductive film 23 is suppressed. Hence, it ispossible to prevent the deterioration in the ferroelectric properties ofthe second ferroelectric film 24 c such as the switching charge amount.

In this way, a ferroelectric film 24 consisting of the first and secondferroelectric films 24 b and 24 c is formed on the first conductive film23.

The second ferroelectric film 24 c formed by the MOCVD method hardlyreduces the switching charge amount Qsw even when the film thicknessthereof is reduced for higher integration. Accordingly, theferroelectric film 24 having the above-described two-layer structure hasan advantage for the higher integration.

Here, it is preferable to form the film thickness of the firstferroelectric film 24 b thinner than the film thickness of the secondferroelectric film 24 c so that the second ferroelectric film 24 formedby the MOCVD method, which is advantageous for the higher integration,constitutes the majority of the ferroelectric film 24.

However, if it is not necessary to achieve the higher integration, it isalso possible to substitute the ferroelectric film 24 with a singlelayer of the PZT film formed by the sputtering method or the sol-gelmethod. As described previously, the sputtering method and the sol-gelmethod are able to form the PZT film at a lower temperature as comparedto the MOCVD method. Accordingly, it is not necessary to provide thefirst ferroelectric film 24 b that serves for preventing the diffusionof the lead atoms by the heat. For this reason, the ferroelectricproperties of the ferroelectric film 24 are not deteriorated even whenthe single-layer PZT film formed by any of these film formation methodsis used as the ferroelectric film 24.

When the ferroelectric film 24 is formed by sputtering method or thesol-gel method as described above, the ferroelectric film 24 issubjected to crystallization annealing to crystallize PZT. During thiscrystallization annealing process, the atoms on the A site thatconstitute the ferroelectric film 24 are thermally diffused downward asdescribed previously. However, the thermal diffusion is blocked by theconductive anti-diffusion film 22, and the detachment of the firstconductive film 23 is thereby prevented.

Subsequently, as show in FIG. 6K, an iridium oxide (IrOx) film servingas a first conductive metal oxide film 25 d is formed with a thicknessof about 50 nm on the ferroelectric film 24 by the sputtering methodwhile the silicon substrate 1 is heated. Note that, the iridium oxidefilm, which is formed by the sputtering method while heating the siliconsubstrate 1 in this manner, is crystallized at the time of filmformation without carrying out the crystallization process.

The conditions for forming the first conductive metal oxide film 25 dare not particularly limited. In this embodiment, the substratetemperature is set at 300° C., and the mixed gas of oxygen at a flowrate of 140 sccm and argon gas at a flow rate of 60 sccm is used as thesputtering gas. Moreover, the sputtering power is set to 1 kW.

Here, when the first conductive metal oxide film 25 d is formed by thesputtering method, the ferroelectric film 24 may be damaged by thesputtering gas, and may cause the lack of the oxygen concentration inthat film. Accordingly, the ferroelectric properties of the film may bedeteriorated.

To deal with this problem, the RTA process is performed in the mixed gasatmosphere of argon and oxygen after the first conductive metal oxidefilm 25 d is formed to recover the damages on the ferroelectric film 24caused by the sputtering processes and to compensate for the lack ofoxygen in the ferroelectric film 24.

The conditions of this RTA process are not particularly limited. In thisembodiment, the substrate temperature is set to 725° C., and theprocessing time period is set to 60 seconds. Furthermore, the flow ofargon and oxygen are set to 2000 sccm and 20 sccm, respectively.

Here, the first conductive metal oxide film 25 d is crystallized at thetime of film formation. Reflecting the crystal grains of the firstconductive metal oxide film 25 d, unevenness is formed in the interfacebetween the first conductive metal oxide film 25 d and the ferroelectricfilm 24. The above RTA process also has an advantage to planarize theunevenness.

In the above-described RTA process, the atoms on the A site constitutingthe ferroelectric film 24, i.e. the lead atoms are thermally diffuseddownward. However, as described previously, the thermal diffusion isinhibited by the conductive anti-diffusion film 22 so that thedetachment or the expansion of the first conductive film 23 does notoccur, which is attributable to the reaction between the lead atoms andthe conductive oxygen barrier film 17.

Next, an iridium oxide film serving as a second conductive metal oxidefilm 25 e is formed with a thickness ranging from about 100 nm to 300nm, for example with a thickness of 200 nm, on the first conductivemetal oxide film 25 d by the sputtering method while the substratetemperature is maintained at room temperature. The second conductivemetal oxide film 25 e is formed in an argon atmosphere at a pressure of0.8 Pa while the sputtering power is set 1.0 kW, and while the filmformation time period is set 79 seconds.

Here, unlike the first conductive metal oxide film 25 d crystallized atthe high film formation temperature, the second conductive metal oxidefilm 25 e is amorphous because the film is formed by the sputteringmethod while the substrate temperature is set to room temperature.

Incidentally, in the above-described iridium oxide sputtering process,the iridium atoms sputtered from the iridium target are oxidized in thesputtering atmosphere, whereby iridium oxide thus formed is deposited onthe substrate. Therefore, some of the deposited iridium oxide may beinsufficiently oxidized in the atmosphere, and the iridium oxide film isapt to contain less oxygen as a whole than that of the stoichiometriccomposition (IrO₂).

However, the catalytic action of the second conductive metal oxide film25 e is enhanced by the lack of oxygen in the second conductive metaloxide film 25 e. Accordingly, hydrogen can be generated as a result ofthe contact of outside moisture with the second conductive metal oxidefilm 25 e. It is necessary to minimize the generation of hydrogen in themanufacturing process of the FeRAM because hydrogen causes the reductionreaction of the ferroelectric film 24, and thereby deteriorates theferroelectric properties thereof.

For this reason, from the viewpoint of preventing the generation ofhydrogen, it is preferable to set the oxygen content of the secondconductive metal oxide film 25 e higher than the oxygen content of thefirst conductive metal oxide film 25 d.

Accordingly, in this embodiment, the proportion of the flow rate ofoxygen is increased at the time of film formation of the secondconductive metal oxide film 25 e as compared to the film formation ofthe first conductive metal oxide film 25 d to render the iridium oxidecomposition of the second conductive metal oxide film 25 e close to thestoichiometric composition (IrO₂), thereby the catalytic action of thesecond conductive metal oxide film 25 e is suppressed.

The second conductive metal oxide film 25 e and the first conductivemetal oxide film 25 d collectively constitute a conductive metal oxidefilm 25 b as shown in FIG. 6K.

Note that, the constituent material of the first and second conductivemetal oxide films 25 d and 25 e is not limited only to iridium oxide.The first and second conductive metal oxide films 25 d and 25 e may bemade of an oxide of any of iridium, ruthenium, rhodium, rhenium, osmium,and palladium. In addition, it is also possible to form the conductivemetal oxide film 25 b by stacking oxides of these elements.

Subsequently, as shown in FIG. 6L, an iridium film serving as aconductivity enhancing film 25 c is formed with a thickness ranging from50 nm to 100 nm on the conductive metal oxide film 25 b by thesputtering method. The sputtering method is carried out in an argonatmosphere at a pressure of 1 Pa, and sputtering power of 1.0 kW isapplied to the sputtering atmosphere.

The conductivity enhancing film 25 c and the conductive metal oxide film25 b located therebelow collectively constitute a second conductive film25. The conductivity enhancing film 25 c serves for compensating for theconductivity of the second conductive film 25 which tends to beinsufficient only by use of the conductive metal oxide film 25 b.Moreover, iridium contained in the conductivity enhancing film 25 c hasa fine barrier property against hydrogen. Accordingly, the conductivityenhancing film 25 c also serves for preventing deterioration in theferroelectric film 24 by blocking outside hydrogen.

Note that, the conductivity enhancing film 25 c may be formed any of aruthenium film, a rhodium film, and a palladium film instead of theiridium film.

Thereafter, the back surface of the silicon substrate 1 is cleaned.

Next, as shown in FIG. 6M, a titanium nitride film is formed on thesecond conductive film 25 by the sputtering method. This titaniumnitride film is formed as a first mask material layer 26.

Moreover, a silicon oxide film serving as a second mask material layer27 is formed on the first mask material layer 26 by the plasma CVDmethod using TEOS gas.

Subsequently, as shown in FIG. 6N, a second hard mask 27 a is formed bypatterning the second mask material layer 27 into an island shape.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 6O will be described below.

First, a first hard mask 26 a is formed by etching the first maskmaterial layer 26 while using the second hard mask 27 a as the mask.

Subsequently, the portions of the respective films 22 to 25 not coveredwith the first and second hard masks 26 a and 27 a are subjected to dryetching.

In this way, the first conductive film 23, the ferroelectric film 24,and the second conductive film 25 are formed into a lower electrode 23a, a capacitor dielectric film 24 a, and an upper electrode 25 a,respectively, and these constituents collectively constitute aferroelectric capacitor Q. Meanwhile, by this dry etching process, theconductive anti-diffusion film 22 is patterned into an island shapewhich is the same planar shape as that of the lower electrode 23 a.

The gas used for the dry etching process is not particularly limited.However, the mixed gas of HBr and oxygen is used as the etching gas forthe conductive anti-diffusion film 22, the first conductive film 23, andthe second conductive film 25. On the other hand, the mixed gas ofchlorine and argon is used as the etching gas for the ferroelectric film24. Note that it is also possible to add C₄F₈ gas to these gases.

Moreover, since the conductive oxygen barrier film 17 has etchingresistance against the etching gas for this conductive anti-diffusionfilm 22, the conductive oxygen barrier film 17 remains on the entiresurface of the conductive adhesive film 16 after the capacitor Q isformed.

The capacitor Q thus formed is electrically connected to the firstconductive plug 32 a via the conductive anti-diffusion film 22, theconductive oxygen barrier film 17, the conductive adhesive film 16, andthe third conductive plug 36 a.

Subsequently, as shown in FIG. 6P, the second hard mask 27 a made ofsilicon oxide is removed by wet etching while using the mixed solutionof hydrogen peroxide (H₂O₂), ammonia, and water as the etching solution.Note that it is also possible to remove the second hard mask 27 a by dryetching.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 6Q will be described below.

First, the conductive adhesive film 16 and the conductive oxygen barrierfilm 17 are etched by use of the first hard mask 26 a as the mask so asto leave these films only below the capacitor Q. This etching process isconducted by dry etching, and the mixed gas of, for example, argon andchlorine is used as the etching gas.

Moreover, since the first hard mask 26 a is also etched by this etchinggas, the first hard mask 26 a is removed when the etching process iscompleted, and consequently the upper surface of the upper electrode 25a is exposed.

Subsequently, as shown in FIG. 6R, an alumina (Al₂O₃) film is formedwith a thickness of about 20 nm so as to cover the capacitor Q. Thealumina film is formed as a first capacitor protection insulating film39. The alumina constituting the first capacitor protection insulatingfilm 39 has an excellent performance to prevent hydrogen transmission.Accordingly, outside hydrogen is blocked by this first capacitorprotection insulating film 39. In this way, it is possible to preventdeterioration in the capacitor dielectric film 24 a attributable tohydrogen.

Here, the capacitor dielectric film 24 a is damaged by the dry etchingprocess (see FIG. 6O) for forming the capacitor Q and by the formationof the first capacitor protection insulating film 39 by the sputteringmethod.

In order to allow the capacitor dielectric film 24 a to recover fromsuch damages, the capacitor dielectric film 24 a is subjected torecovery annealing in an oxygen-containing atmosphere as shown in FIG.6S. The conditions for this recovery annealing process are notparticularly limited. However, in this embodiment, the substratetemperature in a furnace is set in a range from 550° C. to 700° C., forexample 650° C., and the annealing process is continued for about 60minutes.

Subsequently, as shown in FIG. 6T, another alumina film is formed with athickness of about 20 nm on the first capacitor protection insulatingfilm 39 by the CVD method. This alumina film is formed as a secondcapacitor protection insulating film 40.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 6U will be described below.

First, a silicon oxide film serving as a second interlayer insulatingfilm 41 is formed on the second capacitor protection insulating film 40by the plasma CVD method using the TEOS gas as reactive gas. Thereactive gas also contains oxygen gas and helium gas. Although the filmthickness of the second interlayer insulating film 41 is notparticularly limited, the film thickness on the flat surface of thesilicon substrate 1 is set 1500 nm in this embodiment.

Note that it is also possible to form an inorganic insulating film asthe second interlayer insulating film 41 instead of the silicon oxidefilm.

Thereafter, the surface of the second interlayer insulating film 41 ispolished and planarized by the CMP method.

Then, the surface of the second interlayer insulating film 41 is exposedto N₂O plasma as a dehydrating process for the second interlayerinsulating film 41. This N₂O plasma removes moisture remaining insidethe second interlayer insulating film 41, and prevents the secondinterlayer insulating film 41 from reabsorbing moisture.

Note that it is also possible to carry out the N₂ plasma process as thedehydrating process.

Subsequently, a flat alumina film is formed with a thickness rangingfrom about 20 nm to 100 nm on the second interlayer insulating film 41by the sputtering method. The alumina film is formed as a thirdcapacitor protection insulating film 42. This third capacitor protectioninsulating film 42 is formed on the planarized second interlayerinsulating film 41, and thus is not required to have an excellentcoverage characteristic. Accordingly, the alumina film is formed by thelow-cost sputtering method as described above. Nevertheless, the methodof forming the third capacitor protection insulating film 42 is notlimited only to the sputtering method, and the CVD method is alsoapplicable thereto.

Thereafter, as shown in FIG. 6V, a silicon oxide film serving as a capinsulating film 43 is formed with a thickness ranging from about 300 nmto 500 nm on the third capacitor protection insulating film 42 by theplasma CVD method using the TEOS gas. Note that it is also possible toform a silicon oxynitride film or a silicon nitride film as the capinsulating film 43 instead.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 6W will be described below.

First, the first to third capacitor protection insulating films 39, 40,and 42, the second interlayer insulating film 41, and the cap insulatingfilm 43 are patterned to form a second hole 41 a through these filmslocated above the upper electrode 25 a.

Subsequently, the silicon substrate 1 is put into an unillustratedfurnace in order to allow the capacitor dielectric film 24 a to recoverfrom damages suffered in the precedent processes. Then, the siliconsubstrate 1 is subjected to recovery annealing for about 40 minutes inan oxygen atmosphere while the substrate temperature is set 550° C.

Next, the first to third capacitor protection insulating films 39, 40,and 42, the second interlayer insulating film 41, the cap insulatingfilm 43, the underlying insulating film 15, and the antioxidantinsulating film 14 located above the second conductive plug 32 b arepatterned to form a third hole 41 b through these films.

Note that the second hole 41 a is covered with a resist pattern duringthis patterning process, and is protected from the etching atmosphere bythe resist pattern.

Here, if an attempt is made to form these holes 41 a and 41 b at thesame time, the upper electrode 25 a in the second hole 41 a is exposedto the etching atmosphere for a long time period until the deep thirdhole 41 b is completely opened. Accordingly, there arises the problem ofdeterioration in the capacitor dielectric film 24 a.

In this embodiment, the second and third holes 41 a and 41 b havingmutually different depths are formed separately as described above. Inthis way, it is possible to avoid such a problem.

Moreover, the second conductive plug 32 b above the second source/drainregion 8 b remains covered with the antioxidant insulating film 14 untilthe completion of this process. It is, therefore, possible to preventthe occurrence of the contact defect attributable to the oxidation oftungsten that constitutes the second conductive plug 32 b.

Subsequently, a titanium film and a titanium nitride film collectivelyserving as a glue film are formed in this order above the cap insulatingfilm 43 and on the inner surfaces of the second and third holes 41 a and41 b by the sputtering method.

Note that it is also possible to form the titanium nitride film by theMOCVD method. In this case, it is preferable to anneal the titaniumnitride film in an atmosphere prepared by converting nitrogen andhydrogen into plasma in order to remove carbon from the titanium nitridefilm. Even when the annealing process is carried out in thehydrogen-containing atmosphere in this manner, the conductivityenhancing film 25 c (see FIG. 6L) made of iridium and formed on theuppermost layer of the upper electrode 25 a blocks hydrogen.Accordingly, there is no chance of the reduction reaction of theconductive metal oxide film 25 b by hydrogen.

Moreover, a tungsten film is formed on the glue film by the CVD methodso as to bury the second and third holes 41 a and 41 b completely withthis tungsten film.

Thereafter, unnecessary portions of the glue film and the tungsten filmon the cap insulating film 43 are polished and removed by the CMPmethod. Accordingly, these films are left only inside the second andthird holes 41 a and 41 b as fourth and fifth conductive plugs 47 a and47 b, respectively.

Of these plugs, the fourth conductive plug 47 a is electricallyconnected to the upper electrode 25 a of the capacitor Q. Meanwhile, thefifth conductive plug 47 b is electrically connected to the secondconductive plug 32 b. The fifth conductive plug 47 b and the secondconductive plug 32 b collectively constitute part of a bit line.

Thereafter, as shown in FIG. 6X, a metal laminated film is formed on thecap insulating film 43 and the conductive plugs 47 a and 47 b by thesputtering method. Then, a metal interconnect 49 a and a bit-lineconductive pad 49 b are formed by patterning this metal laminated film.

The metal laminated film is formed by stacking a titanium film with athickness of 60 nm, a titanium nitride film with a thickness of 30 nm, acopper-containing aluminum film with a thickness of 360 nm, anothertitanium film with a thickness of 5 nm, and another titanium nitridefilm with a thickness of 70 nm in this order.

In this way, the basic structure of the semiconductor device of thisembodiment is completed.

According to the above-described embodiment, the conductiveanti-diffusion film 22 is formed between the conductive oxygen barrierfilm 17 and the lower electrode 23 a as shown in FIG. 6X. Therefore, thethermal diffusion of the lead atoms in the ferroelectric film 24 isblocked by the conductive anti-diffusion film 22 at the time ofperforming the annealing processes after the formation of the firstconductive film 23 such as the crystallization annealing process for thefirst ferroelectric film 24 b or the annealing process for the firstconductive metal oxide film 25 d constituting the upper electrode 25 a.As a result, the lead atoms do not reach the conductive oxygen barrierfilm 17, and thus it is possible to prevent detachment and expansion ofthe first conductive film 23 attributable to the reaction between thelead atoms and the conductive oxygen barrier film 17, and thereby theproduct yields of semiconductor devices are improved.

Here, the material of the conductive anti-diffusion film 22 is notlimited only to the conductive metal nitride such as titanium nitride aslong as the material can prevent diffusion of the element on the A siteof the ferroelectric film 24, namely the lead atoms.

In particular, iridium and ruthenium have an excellent anti-diffusionfunction against the lead atoms. Therefore, an alloy containing any ofthese elements is usable as the material of the conductiveanti-diffusion film 22. In this case, the conductive anti-diffusion film22 may be formed with a thickness ranging from about 30 nm to 100 nm.

Here, the reason for setting the lower limit of the thickness to 30 nmis that the barrier property against the lead atoms is reduced if thefilm is thinner than 30 nm. Moreover, the reason for setting the upperlimit of the thickness to 100 nm is that it is difficult to etch theconductive anti-diffusion film 22 show in FIG. 6O if the film is thickerthan 100 nm.

Examples of the alloy containing any of iridium and ruthenium include analloy of either iridium or ruthenium with at least one element selectedfrom the groups consisting of tungsten, tantalum, platinum, rhodium,rhenium, gold, and osmium.

Among them, tungsten is a material extremely susceptible to oxidation ifused as a single body, but is hardly oxidized when used as the alloywith iridium or ruthenium. For this reason, contact defects as concernedin JP-A Hei 6 (1994)-326270 hardly occur in the case of using such analloy as the conductive anti-diffusion film 22.

Meanwhile, in addition to titanium nitride, the conductive metal nitrideusable as the material of the conductive anti-diffusion film 22 mayinclude zirconium nitride, hafnium nitride, tantalum nitride, chromiumnitride, and niobium nitride. The conductive anti-diffusion film 22 maybe made of any of these materials.

When constructing the conductive anti-diffusion film 22 from theconductive metal nitride, it is preferable to set the thickness of thefilm equal to or above 10 nm because the barrier property against thelead atoms is reduced if the thickness is below 10 nm.

Note that it is also conceivable to construct the conductiveanti-diffusion film 22 from oxide. However, if the conductiveanti-diffusion film 22 is made of oxide, there is the risk of contactdefects attributable to the oxidation of the third conductive plugs 36 abelow the conductive anti-diffusion film 22 by oxygen therein. It is,therefore, preferable to form the conductive anti-diffusion film 22 madeof the conductive material other than oxides, which is capable ofpreventing the diffusion of the constituent element of the capacitordielectric film 24 a, such as the alloy containing any of iridium andruthenium or the conductive metal nitrides mentioned above.

Moreover, as to the film thicknesses of the conductive anti-diffusionfilm 22 and the lower electrode 23 a, it is preferable to set thethickness of the lower electrode 23 a greater than the thickness of theconductive anti-diffusion film 22 as described in this embodiment. Thisis because the fluctuation in the crystalline orientation of the lowerelectrode 23 a associated with the lattice mismatch with the conductiveanti-diffusion film 22 hardly occurs on the upper surface of the lowerelectrode 23 a, and thus it is easier to align the crystallineorientation of the capacitor dielectric film 24 a in the (111) directionby forming the lower electrode 23 a with the greater thickness than thatof the conductive anti-diffusion film 22.

Moreover, by using the conductive crystal material such as titaniumnitride having the same (111) orientation as that of the capacitordielectric film 24 a as the material of the conductive anti-diffusionfilm 22, it is possible to orient the capacitor dielectric film 24 afavorably in the (111) direction that maximizes the polarization amount.

Meanwhile, as to the capacitor dielectric film 24 a, the firstferroelectric film 24 b is formed in advance by the sputtering methodprior to the formation of the second ferroelectric film 24 c by theMOCVD method. Therefore, the first conductive film 23 is not abnormallyoxidized even when the silicon substrate 1 is heated in the oxygenatmosphere at the time of forming the second ferroelectric film 24 c.

It is, therefore, possible to prevent the surface roughness of thesecond ferroelectric film 24 c caused by the abnormal oxidation of thefirst conductive film 23, and thereby it is possible to form the secondferroelectric film 24 c having the smooth surface morphology. Inaddition, the fluctuation in the crystalline orientation of the secondferroelectric film 24 c partially attributable to the abnormal oxidationis also suppressed. Accordingly, it is possible to provide the methodfor manufacturing a semiconductor device suitable for mass production ofFeRAMs.

According to these features, this embodiment can provide thesemiconductor device including the highly reliable capacitor Q.

(3) Second Embodiment

FIGS. 7A to 7L are cross-sectional views showing states in the course ofmanufacturing a semiconductor device according to a second embodiment ofthe present invention. In the drawings, the constituents described inthe first embodiment are indicated with the same reference numerals asthose in the first embodiment, and the explanations thereof will beomitted hereinafter.

In the process shown in FIG. 6C of the first embodiment, the thirdconductive plug 36 a is formed by polishing the glue film 35 and theplug conductive film 36 by the CMP method.

However, relative to the slurry used in the CMP process, the polishingspeed of the glue film 35 and the plug conductive film 36 are fasterthan that of the underlying insulating film 15 located therebelow.Accordingly, it is difficult to align the levels of the upper surfacesof the third conductive plugs 36 a and the underlying insulating film15, respectively, at the time of completing the CMP process.

For this reason, recesses 15 b are actually formed on the underlyinginsulating film 15 after the CMP process as shown in FIG. 7A, and thelevels of the upper surfaces of the third conductive plugs 36 a becomelower than that of the underlying insulating film 15. The depth of eachrecess 15 b is in a range from 20 nm to 50 nm, and is typically around50 nm.

However, if the recesses 15 b are present, the crystalline orientationof the lower electrode 23 a and the capacitor dielectric film 24 a isare fluctuated. As a consequence, there arises the problem ofdeterioration in the ferroelectric properties of the capacitordielectric film 24 a.

This embodiment applies the following processes to solve this problem.

First, as shown in FIG. 7B, the underlying insulating film 15 issubjected to the ammonia plasma process so as to bond the NH groups tothe oxygen atoms on the surface of the underlying insulating film 15.

In this ammonia plasma process, a parallel-plate plasma reactor is used.The reactor includes an opposing electrode which is located in aposition just about 9 mm (350 mils) away from the silicon substrate 1,for example. Then, the process is executed by supplying ammonia gas intoa chamber at a flow rate of 350 sccm while maintaining the substratetemperature at 400° C. under a pressure of 266 Pa (2 Torr), andsupplying high-frequency power of 100 W at a frequency of 13.56 MHz tothe silicon substrate 1 while supplying high-frequency power of 55 W ata frequency of 350 kHz to the above-mentioned opposing electrode for 60seconds.

Subsequently, a titanium film serving as a planarization conductive film50 is formed with a thickness ranging from 100 nm to 300 nm, for examplewith a thickness of about 100 nm on the underlying insulating film 15and the third conductive plugs 36 a as shown in FIG. 7C so as to burythe recesses 15 b completely with this planarization conductive film 50.

The conditions for forming this planarization conductive film 50 are notparticularly limited. However, in this embodiment, the planarizationconductive film 50 is formed by use of the sputter chamber configured toset a distance between the silicon substrate 1 and a titanium targetequal to 60 mm, and by applying sputtering DC power at 2.6 kW for 35seconds in an argon atmosphere at a pressure of 0.15 Pa while settingthe substrate temperature equal to 20° C.

Moreover, the NH groups are bonded to the oxygen atoms on the surface ofthe underlying insulating film 15 by carrying out the ammonia plasmaprocess (FIG. 7B) before the planarization conductive film 50 is formed.Accordingly, the titanium atoms deposited on the underlying insulatingfilm 15 are hardly captured by the oxygen atoms on the surface of theunderlying insulating film 15. As a result, the titanium atoms can movefreely on the surface of the underlying insulating film 15, and it istherefore possible to form the planarization conductive film 50 made oftitanium which is highly self-organized in the (002) direction.

Note that the planarization conductive film 50 is not only limited tothe titanium film. It is also possible to form any of a tungsten film, asilicon film, and a copper film as the planarization conductive film 50.

Thereafter, the planarization conductive film 50 is subjected to RTA ina nitrogen atmosphere at a substrate temperature of 650° C. In this way,the planarization conductive film 50 made of titanium is nitrogenized,whereby the planarization conductive film 50 is formed of titaniumnitride and oriented in the (111) direction.

Here, concave portions are formed on the upper surface of theplanarization conductive film 50 which are caused by the recesses 15 bformed on the underlying insulating film 15 around the third conductiveplugs 36 a as described previously. If such concave portions are formed,there is the risk of deterioration in the crystallinity of theferroelectric film to be formed above the planarization conductive film50 afterward.

Accordingly, in this embodiment, the upper surface of the planarizationconductive film 50 is polished and planarized by the CMP process, andthe concave portions are removed as shown in FIG. 7D. The slurry to beused in this CMP process is not particularly limited. However, in thisembodiment SSW2000 manufactured by Cabot Microelectronics Corporation isused.

The thickness of the planarization conductive film 50 after the CMPprocess varies in the surface of the silicon substrate or among thesilicon substrates due to polishing errors. In consideration of suchvariation, this embodiment sets a target value for the thickness of theplanarization conductive film 50 after the CMP process in a range from50 nm to 100 nm, or more preferably 50 nm by controlling a polishingperiod.

Incidentally, after the planarization conductive film 50 is subjected tothe CMP process in this manner, crystals located near the upper surfaceof the planarization conductive film 50 are distorted by polishing. Ifthe lower electrode of the capacitor is formed above the planarizationconductive film 50 having the distorted crystals, the lower electrodewill exploit the distortion, and the crystallinity of the lowerelectrode will be deteriorated. Eventually, the ferroelectric propertiesof the ferroelectric film on the lower electrode will be deteriorated.

To avoid such a problem, in the next process, the upper surface of theplanarization conductive film 50 is exposed to ammonia plasma as shownin FIG. 7E so as to prevent the transfer of the crystal distortion onthe polarization conductive film 50 to the film located thereon.

Next, as shown in FIG. 7F, an iridium film serving as a conductiveadhesive film 51 is formed on the planarization conductive film 50 bythe sputtering method after the crystal distortion is resolved by theammonia plasma process. The conductive adhesive film 51 functions as afilm for enhancing adhesion strength between the upper film and thelower film. It is desirable to set the thickness of the conductiveadhesive film 51 as thin as possible. Specifically, it is desirable toform the film, for example, with a thickness equal to or below 20 nm, ormore preferably in a range from 5 nm to 10 nm.

Subsequently, the films 16, 17, and 22 to 25 are stacked as shown inFIG. 7G by executing the processes described with reference to FIGS. 6Eto 6L in the first embodiment.

Note that, in these processes, the conductive anti-diffusion film 22made of titanium nitride is formed between the conductive oxygen barrierfilm 17 and the first conductive film 23 as in the case of the firstembodiment. Therefore, it is possible to prevent the lead atoms in theferroelectric film 24 made of PZT from being thermally diffused andreaching the conductive oxygen barrier film 17, and thereby it ispossible to suppress the detachment of the first conductive film 23caused by the reaction between the lead and the conductive oxygenbarrier film 17.

Subsequently, the first mask material layer 26 and the second hard mask27 a are formed on the second conductive film 25 as shown in FIG. 7H byexecuting the processes described with reference to FIGS. 6M and 6N.

Next, the first hard mask 26 a is formed as shown in FIG. 7I by etchingthe first mask material layer 26 while using the second hard mask 27 aas the mask.

Thereafter, portions of the second conductive film 25, the ferroelectricfilm 24, the first conductive film 23, and the conductive anti-diffusionfilm 22 not covered with the first and second hard masks 26 a and 27 aare subjected to dry etching. In this way, the capacitor Q including thelower electrode 23 a, the capacitor dielectric film 24 a, and the upperelectrode 25 a is formed, and the conductive anti-diffusion film 22 ispatterned into an island shape below the lower electrode 25 a.

In this etching process, as in the case of the first embodiment, themixed gas of HBr and oxygen is used as the etching gas for the firstconductive film 23, the second conductive film 25, and the conductiveanti-diffusion film 22. Meanwhile, the mixed gas of chlorine and argonis used as the etching gas for the ferroelectric film 24.

Subsequently, as shown in FIG. 7J, the second hard mask 27 a made ofsilicon oxide is removed by wet etching while using the mixed solutionof hydrogen peroxide, ammonia, and water as the etching solution. Notethat it is also possible to remove the second hard mask 27 a by dryetching.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 7K will be described below.

First, the conductive anti-diffusion film 22, the conductive oxygenbarrier film 17, the conductive adhesive film 16, the conductiveadhesive film 51, and the planarization conductive film 50 are etched byusing the first hard mask 26 a as the mask so as to leave these filmsonly below the capacitor Q. This etching process is conducted by dryetching, and the mixed gas of argon and chlorine is used as the etchinggas, for example.

Moreover, since the first hard mask 26 a is also etched by this etchinggas, the first hard mask 26 a is removed when the etching process iscompleted. Consequently, the upper surface of the upper electrode 25 ais exposed.

Thereafter, the basic structure of the semiconductor device of thisembodiment is completed as shown in FIG. 7L by executing the processesdescribed with reference to FIGS. 6R to 6X in the first embodiment.

According to this embodiment as described with reference to the FIG. 7C,the recesses 15 b generated around the third conductive plugs 36 a as aresult of the CMP process are buried with the planarization conductivefilm 50, and the planarization conductive film 50 is further planarizedby another CMP process.

In this way, the lower electrode 23 a (see FIG. 7L) formed above theplanarization conductive film 50 can achieve fine planarity, and thecrystalline orientation of the lower electrode 23 a is thereby improved.Moreover, the crystalline orientation of the capacitor dielectric film24 a is also improved by way of the improved crystalline orientation ofthe lower electrode 23 a. Accordingly, the ferroelectric properties ofthe capacitor dielectric film 24 a such as the switching charge amountare enhanced.

Moreover, the conductive anti-diffusion film 22 is disposed between theconductive oxygen barrier film 17 and the first conductive film 23 as inthe case of the first embodiment. Accordingly, it is possible to preventthe diffusion of the lead atoms in the ferroelectric film 24 toward theconductive oxygen barrier film 17 due to the heat supplied at the timeof forming the capacitor Q, and thereby the detachment or the expansionof the first conductive film 23 attributable to the chemical reactionbetween the lead and the conductive oxygen barrier film 17 is prevented.

(4) Third Embodiment

FIG. 8 is a cross-sectional view of a semiconductor device according tothis embodiment.

This embodiment is different from the second embodiment in that theplanarization conductive film 50 is partially removed from the uppersurface of the underlying insulating film 15 in the CMP process shown inFIG. 7D so as to leave only the portion of the planarization conductivefilm 50 located on the third conductive plug 36 a inside the recess 15b. Other features of this embodiment are the same as those in the secondembodiment.

Even when the planarization conductive film 50 is completely removedfrom the upper surface of the underlying insulating film 15 by the CMPprocess in this manner, it is possible to reduce the over-polishingamount at the time of the CMP process since the planarization conductivefilm 50 has the small film thickness. Accordingly, a concave portion ishardly formed on the upper surface of the planarization conductive film50 left inside the recess 15 b. Thus, the upper surfaces of theplanarization conductive film 50 and of the underlying insulating film15 constitute the continuous flat surface. As a result, thecrystallinity each of the lower electrode 23 a and the capacitordielectric film 24 a becomes favorable.

In addition, the conductive anti-diffusion film 22 is formed below thelower electrode 23 a in this embodiment as well. Accordingly, it ispossible to prevent the detachment or the expansion of the lowerelectrode 23 a caused by the thermal diffusion of the lead atoms fromthe capacitor dielectric film 24 a made of PZT toward the conductiveoxygen barrier film 17.

(5) Fourth Embodiment

FIGS. 9A to 9Q are cross-sectional views showing states in the course ofmanufacturing a semiconductor device according to this embodiment. Inthe drawings, the constituents described in the first embodiment areindicated with the same reference numerals as those in the firstembodiment, and the explanations thereof will be omitted hereinafter.

In the beginning, processes to be conducted prior to obtaining across-sectional structure shown in FIG. 9A will be described below.

First, the cover insulating film 10 and the first interlayer insulatingfilm 11 are formed on the silicon substrate 1 in accordance with thesteps described in the first embodiment with reference to FIG. 6A. Then,contact holes are formed above the first source/drain regions 8 a bypatterning these insulating films.

Moreover, the glue film and the tungsten film are sequentially formedinside the contact hole, and thereafter the excessive glue film and theexcessive tungsten film on the first interlayer insulating film 11 arepolished and removed by the CMP method. These films are left only insidethe contact hole as the first conductive plug 32 a.

Next, a titanium film is formed with a thickness of about 20 nm on eachof the first interlayer insulating film 11 and the first conductive plug32 a as shown in FIG. 9B. This titanium film is formed as the conductiveadhesive film 16.

Note that, it is also possible to execute the ammonia plasma process inadvance on the upper surfaces of the first interlayer insulating film 11and of the first conductive plugs 32 a before this conductive adhesivefilm 16 is formed. By executing the ammonia plasma process, the titaniumatoms deposited on the first interlayer insulating film 11 are hardlycaptured by the oxygen atoms on the surface of the insulating film 11.Accordingly, the titanium atoms can move freely on the surface of thefirst interlayer insulating film 11, and it is therefore possible toform the conductive adhesive film 16 made of titanium which is highlyself-organized in the (002) direction.

Thereafter, the conductive adhesive film 16 is subjected to RTA in anitrogen atmosphere at a substrate temperature of 650° C. for aprocessing period of 60 seconds. In this way, the conductive adhesivefilm 16 made of the titanium is nitrogenized, whereby the conductiveadhesive film 16 is formed of the titanium nitride which is oriented inthe (111) direction.

Moreover, a titanium aluminum nitride film functioning as the conductiveoxygen barrier film 17 is formed with a thickness of 100 nm on thisconductive adhesive film 16 by the reactive sputtering method.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 9C will be described below.

First, a titanium film is formed with a thickness of about 50 nm on theconductive oxygen barrier film 17 by the sputtering method while thefilm formation conditions identical to those of the first embodiment isadopted. This titanium film is formed as the conductive anti-diffusionfilm 22.

Moreover, the titanium in the conductive anti-diffusion film 22 isnitrogenized by executing the RTA process in the nitrogen atmosphere,thereby the conductive anti-diffusion film 22 made of the titaniumnitride is oriented in the (111) direction. The RTA process is executedwhile the substrate temperature is set to 650° C., for example.

Subsequently, a platinum film serving as the first conductive film 23 isformed with a thickness of about 100 nm on this conductiveanti-diffusion film 22 by the sputtering method.

Thereafter, the first conductive film 23 is subjected to RTA in theargon atmosphere for 60 seconds while the substrate temperature is setequal to or above 650° C. By performing this RTA process, the adhesionamong the first conductive film 23, the conductive anti-diffusion film22, and the conductive oxygen barrier film 17 is enhanced, and thecrystallinity of the first conductive film 23 is also improved.

Subsequently, as shown in FIG. 9D, a thin PZT film serving as the firstferroelectric film 24 b is formed with a thickness ranging from about 1nm to 50 nm on the first conductive film 23 by the sputtering method.Note that it is possible to form the first ferroelectric film 24 b bythe sol-gel method instead.

Here, it is also possible to add any of lanthanum, calcium, strontium,and niobium to the PZT that constitutes the first ferroelectric film 24b in order to improve the electrical characteristics of the firstferroelectric film 24 b.

Moreover, the material of the first ferroelectric film 24 b is notlimited only to PZT. It is possible to form the first ferroelectric film24 b by use of the ferroelectric material having an ABO₃-type perovskitestructure (in which A is any one selected from the group consisting ofBi, Pb, Ba, Sr, Ca, Na, K and any of rare earth elements, and B is anyone selected from the group consisting of Ti, Zr, Nb, Ta, W, Mn, Fe, Coand Cr) such as BLT.

In addition, Bi layer structure compounds such as (Bi_(1−x)R_(x))Ti₃O₁₂(in which R is a rare earth element and 0<x<1), SrBi₂Ta₂O₉ (SBT),SrBi₄Ti₄O₁₅ and the like are usable as the constituent material of thefirst ferroelectric film 24 b since these substances have the ABO₃-typeperovskite structure when seen as one unit of crystal.

Here, the first ferroelectric film 24 b formed by the sputtering methodor the sol-gel method is not crystallized at the time of film formation.

Accordingly, in the next step, the first ferroelectric film 24 b issubjected to crystallization annealing as shown in FIG. 9E, whereby thePZT in the first ferroelectric film 24 b is crystallized and oriented inthe (111) direction. Note that, the conditions for this crystallizationannealing process are the same as the conditions described withreference to FIG. 6I in the first embodiment, and the explanationthereof will be omitted herein.

Subsequently, as shown in FIG. 9F, a PZT film is formed with a thicknessof about 80 nm on the first ferroelectric film 24 b by the MOCVD method.The PZT film is formed as the second ferroelectric film 24 c. As theconditions for forming the second ferroelectric film 24 c, theconditions described with reference to FIG. 6J in the first embodimentmay be adopted for an example.

The ferroelectric films 24 b and 24 c thus formed collectivelyconstitute the ferroelectric film 24.

Subsequently, as show in FIG. 9G, the first conductive metal oxide film25 d and the second conductive metal oxide film 25 e which are made ofiridium oxide are formed on the ferroelectric film 24 by executing theprocesses described with reference to FIG. 6K in the first embodiment.These films collectively constitute the conductive metal oxide film 25b.

Moreover, as shown in FIG. 9H, an iridium film serving as theconductivity enhancing film 25 c is formed with a thickness ranging from50 nm to 100 nm on the conductive metal oxide film 25 b by thesputtering method, while the film formation conditions identical tothose of the first embodiment are used.

Then, the conductivity enhancing film 25 c and the conductive metaloxide film 25 b collectively constitute the second conductive film 25.

Next, as shown in FIG. 9I, the first mask material layer 26 made oftitanium nitride is formed on the second conductive film 25 by thesputtering method.

Moreover, the second hard mask 27 a is formed by forming a silicon oxidefilm on the first mask material layer 26 by the plasma CVD method usingTEOS gas, and then patterning the silicon oxide film.

Subsequently, as shown in FIG. 9J, the first hard mask 26 a is formed byetching the first mask material layer 26 while using the second hardmask 27 a as the mask.

Next, the portions of the second conductive film 25, the ferroelectricfilm 24, the first conductive film 23, and the conductive anti-diffusionfilm 22 not covered with the first and second hard masks 26 a and 27 aare subjected to dry etching. In this way, the capacitor Q including thelower electrode 23 a, the capacitor dielectric film 24 a, and the upperelectrode 25 a is formed, and the conductive anti-diffusion film 22 isleft in an island shape below the lower electrode 23 a.

Note that, the conditions for this dry etching process are describedwith reference to FIG. 6O in the first embodiment, and the explanationthereof will be omitted herein.

Meanwhile, the conductive oxygen barrier film 17 is not etched by theabove-described dry etching process, and consequently remains on theentire surface of the conductive adhesive film 16.

Next, as shown in FIG. 9K, the second hard mask 27 a is removed by wetetching or dry etching. In the case of wet etching, the mixed solutionof hydrogen peroxide, ammonia, and water is used as the etchingsolution.

Subsequently, processes to be conducted prior to obtaining across-sectional structure shown in FIG. 9L will be described below.

First, the conductive adhesive film 16 and the conductive oxygen barrierfilm 17 are subjected to dry etching by use of the first hard mask 26 aas the mask and the mixed gas of argon and chlorine as the etching gasso as to leave these films only below the capacitor Q.

Note that, since the first hard mask 26 a is also etched by this etchinggas, the first hard mask 26 a is removed when the etching process iscompleted, and consequently the upper surface of the upper electrode 25a is exposed.

Subsequently, as shown in FIG. 9M, an alumina film serving as the firstcapacitor protection insulating film 39 is formed with a thickness ofabout 20 nm on the entire upper surface of the silicon substrate 1 so asto protect the capacitor Q against reductive substances such ashydrogen.

Then, in order to allow the capacitor dielectric film 24 a to recoverfrom the damages caused by dry etching (see FIG. 9J) for forming thecapacitor Q and by the sputtering method at the time of forming thefirst capacitor protection insulation film 39, the capacitor dielectricfilm 24 a is subjected to recovery annealing in an oxygen-containingatmosphere. As to the conditions for this recovery annealing process,the substrate temperature in the furnace is set in a range from 550° C.to 700° C., for example 650° C., and the annealing process is continuedfor about 60 minutes.

Thereafter, another alumina film is formed with a thickness of about 20nm on the first capacitor protection insulating film 39 by the CVDmethod. This alumina film is formed as the second capacitor protectioninsulating film 40.

Subsequently, as shown in FIG. 9N, a silicon oxide film serving as thesecond interlayer insulating film 41 is formed on the second capacitorprotection insulating film 40 by the plasma CVD method using the TEOSgas as the reactive gas. The reactive gas also contains oxygen gas andhelium gas. The second interlayer insulating film 41 has a thickness of1500 nm on the flat surface of the silicon substrate 1.

Note that, it is also possible to form an inorganic insulating film asthe second interlayer insulating film 41 instead of the silicon oxidefilm.

Thereafter, the surface of the second interlayer insulating film 41 ispolished and planarized by the CMP method.

Next, processes to be conducted prior to obtaining a cross-sectionalstructure shown in FIG. 9O will be described below.

First, the surface of the second interlayer insulating film 41 isexposed to N₂O plasma to remove the moisture remaining inside the secondinterlayer insulating film 41, and to prevent the second interlayerinsulating film 41 from reabsorbing moisture.

Note that, it is also possible to carry out the N₂ plasma process as thedehydrating process.

Subsequently, the cover insulating film 10, the first and secondinterlayer insulating films 11 and 41, and the first and secondcapacitor protection insulating films 39 and 40 are patterned to form afirst hole 41 c through these insulating films located above the secondsource/drain region 8 b.

Then, a glue film and a tungsten film are sequentially formed insidethis first hole 41 c, and thereafter the excessive portions of the gluefilm and the tungsten film on the second interlayer insulating film 41is polished and removed by the CMP method. Consequently, these films areleft only inside the first hole 41 c collectively as a second conductiveplug 54.

The second conductive plug 54 constitutes part of a bit line, and iselectrically connected to the second source/drain region 8 b.

Incidentally, the second conductive plug 54 mainly contains tungstenwhich is susceptible to oxidation, and consequently is apt to cause acontact defect if tungsten is oxidized during the process.

To deal with this problem, a silicon oxynitride film is formed with athickness of about 100 nm on the upper surfaces of the second interlayerinsulating film 41 and the second conductive plug 54 to prevent theoxidation of the second conductive plug 54. This silicon oxynitride filmis formed as an antioxidant insulating film 55.

Next, as shown in FIG. 9P, the first and second capacitor protectioninsulating films 39 and 40, the second interlayer insulating film 41,and the antioxidant insulating film 55 are patterned to form a secondhole 41 d through these insulating films located above the upperelectrode 25 a.

After forming the second hole 41 d, it is also possible to execute theannealing process in an oxygen-containing atmosphere so as to allow thecapacitor dielectric film 24 a to recover from the damages caused by theprecedent processes. Even when such an annealing process is executed,the oxidation of the second conductive plug 54 is prevented by theantioxidant insulating film 55.

Thereafter, the antioxidant insulating film 55 is etched back andremoved.

Subsequently, as shown in FIG. 9Q, a metal laminated film is formed onthe upper surfaces of the second interlayer insulating film 41 and thesecond conductive plug 54 by the sputtering method. A metal interconnect57 a and a bit-line conductive pad 57 b are formed by patterning thismetal laminated film.

The metal laminated film is formed by stacking, for example, a titaniumfilm with a thickness of 60 nm, a titanium nitride film with a thicknessof 30 nm, a copper-containing aluminum film with a thickness of 400 nm,another titanium film with a thickness of 5 nm, and another titaniumnitride film with a thickness of 70 nm in this order.

In this way, the basic structure of the semiconductor device of thisembodiment is completed.

According to the above-described embodiment, it is possible to simplifythe processes as compared to the first embodiment because the thirdconductive plugs 36 a and the underlying insulating film 15 are notformed unlike the first embodiment.

Moreover, the second conductive plug 54 constituting the part of the bitline above the second source/drain region 8 b has only single stage.This is a simpler structure than that of the first embodiment in whichtwo stages of the conductive plugs 32 b and 47 b are formed.

In addition, the conductive anti-diffusion film 22 is disposed betweenthe lower electrode 23 a and the conductive oxygen barrier film 17 as inthe case of the first embodiment. Accordingly, it is possible to preventthe thermal diffusion of the lead atoms in the capacitor dielectric film24 a by the conductive anti-diffusion film 22 when forming the capacitorQ, and thereby the detachment or the expansion of the lower electrode 23a attributable to the chemical reaction is prevented between the leadand the conductive oxygen barrier film 17.

As described above, according to the present invention, the conductiveanti-diffusion film is disposed between the lower electrode and theconductive oxygen barrier film. It is, therefore, possible to preventthe thermal diffusion of the constituent element of the capacitordielectric film by use of the conductive anti-diffusion film. In thisway, it is possible to prevent the detachment of the lower electrodeattributable to the chemical reaction with the constituent element, andthereby the semiconductor device including the highly reliable capacitoris provided.

The foregoing is considered as illustrative only of the principles ofthe present invention. Further, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and applications shown anddescribed, and accordingly, all suitable modifications and equivalentsmay be regarded as falling within the scope of the invention in theappended claims and their equivalents.

1. A method for manufacturing a semiconductor device comprising: forminga first impurity diffusion region in a semiconductor substrate; forminga first interlayer insulating film over the semiconductor substrate;forming a first hole in the first interlayer insulating film; forming, aplug conductive film in the first hole, to form a first conductive plugelectrically connected to the first impurity diffusion region; forming aconductive oxygen barrier film on each of the first interlayerinsulating film and the first conductive plug; forming a conductiveanti-diffusion film above the conductive oxygen barrier film; forming,above the conductive anti-diffusion film, a first conductive film;forming a ferroelectric film on the first conductive film; forming asecond conductive film on the ferroelectric film; patterning theconductive anti-diffusion film, the first conductive film, theferroelectric film and second conductive film; and removing the regionof the conductive oxygen barrier film uncovered with the patterned firstconductive film, wherein a film made of a non-oxide conductive materialfor preventing the diffusion of a constituent element of theferroelectric film is formed as the conductive anti-diffusion film. 2.The method for manufacturing a semiconductor device according to claim1, wherein the process of forming the ferroelectric film comprises:forming a first ferroelectric film on the first conductive film by anyof a sputtering method and a sol-gel method; annealing and crystallizingthe first ferroelectric film; forming a second ferroelectric film on thefirst ferroelectric film by a metal-organic chemical vapor depositionmethod.
 3. The method for manufacturing a semiconductor device accordingto claim 2, wherein, in the process of forming the second ferroelectricfilm, the semiconductor substrate is heated in an oxygen-containingatmosphere, and then the second ferroelectric film is formed in a rawmaterial gas atmosphere.
 4. The method for manufacturing a semiconductordevice according to claim 3, wherein the first ferroelectric film isexposed to a solvent gas atmosphere after the semiconductor substrate isheated and before the second ferroelectric film is formed.
 5. The methodfor manufacturing a semiconductor device according to claim 4, wherein afilm having an ABO₃-type perovskite structure is formed as the capacitordielectric film, in which A is any one selected from the groupconsisting of Bi, Pb, Ba, Sr, Ca, Na, K and any of rare earth elements,and in which B is any one selected from the group consisting of Ti, Zr,Nb, Ta, W, Mn, Fe, Co and Cr, and a film for preventing the diffusion ofan element from the A site of the capacitor dielectric film is formed asthe conductive anti-diffusion film.
 6. The method for manufacturing asemiconductor device according to claim 1, wherein the process offorming the second conductive film comprises: forming a first conductivemetal oxide film on the ferroelectric film; annealing the firstconductive metal oxide film; forming, on the first conductive metaloxide film, a second conductive metal oxide film having a larger oxygencontent than that of the first conductive metal oxide film after theannealing process.
 7. The method for manufacturing a semiconductordevice according to claim 1, further comprising: forming an underlyinginsulating film on the first interlayer insulating film and the firstconductive plug; forming a second hole in the underlying insulating filmlocated over the first conductive plug; forming, in the second hole, asecond conductive plug electrically connected to the first conductiveplug; forming a planarization conductive film on each of the secondconductive plug and the underlying insulating film; and planarizing theplanarization conductive film, wherein the conductive oxygen barrierfilm is formed on the planarized planarization conductive film in theprocess of forming the conductive oxygen barrier film.
 8. The method formanufacturing a semiconductor device according to claim 7, wherein, inthe process of planarizing the planarization conductive film, theplanarization conductive film is left only on the second conductive plugby polishing the planarization conductive film.
 9. The method formanufacturing a semiconductor device according to claim 1, furthercomprising: forming a second impurity diffusion region in thesemiconductor substrate; forming a second interlayer insulating filmcovering the capacitor; forming a third hole in the first interlayerinsulating film and the second interlayer insulating film located abovethe second impurity diffusion region; and forming, in the third hole, athird conductive plug electrically connected to the second impuritydiffusion region.